It is often necessary to distribute high-speed signals, such as high-speed differential signals, from one circuit device, such as an integrated circuit or printed circuitboard, to another such circuit device. This may require capacitive or “AC” coupling.
Typically, high-speed signals requiring such AC coupling are routed within internal layers of multi-layered substrates of printed circuitboards or integrated circuits, as known in the art. To provide AC-coupling, coupling or blocking capacitors are used which are mounted on the circuit device substrates (printed circuitboard). To permit the high-speed signals access to the AC blocking capacitors, the signals must be brought to the surface layers of the circuit devices through vias. These vias can have a significant deleterious effect on the signal quality and integrity, especially for high-speed signals having frequencies in the multiple gigabit range. In addition, the adverse signal quality effects increase as the circuit device substrate thickness increases.
Unless preventative measures are taken, the problem will only worsen. As signal rate increases, signal energy content increases, and signal frequency increases, the adverse effects of the vias will prove even more difficult to deal with.
Previous solutions have included ignoring the problem and living with the detrimental effects caused by the vias. Another solution has been to use blind or buried vias where the vias only extend partially through the circuit device substrates. Unfortunately, this increases manufacturing costs of the circuit devices. Another solution has been to back drill the vias to remove unused portions of the vias. This also results in increased manufacturing costs.
The present invention provides a solution to the above-noted problems. As will be seen subsequently, the present invention permits signals to be distributed from one circuit device to another while negating the need for the previously employed vias for accessing surface mounted AC blocking capacitors.